System architecture for a blended braking system in a hybrid powertrain system

ABSTRACT

An engine and a second power generating device transmit power through a transmission to a driveline to a wheel. A control module determines a regenerative braking axle torque capacity and a regenerative braking torque. Power output from the second power generating device is controlled based upon a regenerative braking axle torque request. A brake control module determines a total braking torque request and generates the regenerative braking axle torque request based upon the total braking torque request, the regenerative braking axle torque capacity, and the regenerative braking torque. The brake control module controls a friction brake.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/985,247 filed on Nov. 4, 2007 which is hereby incorporated herein by reference.

TECHNICAL FIELD

This disclosure pertains to control systems for hybrid powertrain systems.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Known hybrid powertrain architectures can include multiple torque-generative devices, including internal combustion engines and non-combustion machines, e.g., electric machines, which transfer torque through a transmission device to an output member. One exemplary hybrid powertrain includes a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving tractive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Machines, operative as motors or generators, can generate torque inputs to the transmission independently of a torque input from the internal combustion engine. The Machines may transform vehicle kinetic energy transmitted through the vehicle driveline to energy that is storable in an energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the hybrid powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the power interchange among the energy storage device and the machines to manage outputs of the transmission, including power, torque and rotational speed.

SUMMARY

An internal combustion engine is mechanically coupled to a transmission device operative to transfer mechanical power between the engine and a second power generating device and an output member mechanically coupled to a driveline to transmit tractive torque to a wheel including an actuable friction brake. A brake control module is operatively connected to the actuable friction brake. A second control module is operatively connected to the internal combustion engine and the transmission device. The second control module is configured to determine a regenerative braking axle torque capacity, determine a regenerative braking torque presently applied to the driveline through the output member of the transmission device, communicate the regenerative braking axle torque capacity and the regenerative braking torque to the brake control module, and generate a control signal to command a power output from the second power generating device based upon a regenerative braking axle torque request. The brake control module is configured to determine a total braking torque request based upon an operator input to a brake pedal, generate the regenerative braking axle torque request based upon the total braking torque request, the regenerative braking axle torque capacity, and the regenerative braking torque, and generate a control signal to control the actuable friction brake based upon the total braking torque request and the regenerative braking torque.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary hybrid powertrain, in accordance with the present disclosure;

FIG. 2 is a schematic diagram of an exemplary architecture for a control system and hybrid powertrain, in accordance with the present disclosure; and

FIGS. 3 and 4 are schematic flow diagrams of a control system architecture for controlling and managing torque in a hybrid powertrain system, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIGS. 1 and 2 depict an exemplary hybrid powertrain. The exemplary hybrid powertrain in accordance with the present disclosure is depicted in FIG. 1, comprising a two-mode, compound-split, electro-mechanical hybrid transmission 10 operatively connected to an engine 14 and torque machines comprising first and second electric machines (‘MG-A’) 56 and (‘MG-B’) 72. The engine 14 and first and second electric machines 56 and 72 each generate power which can be transferred to the transmission 10. The power generated by the engine 14 and the first and second electric machines 56 and 72 and transferred to the transmission 10 is described in terms of input and motor torques, referred to herein as T_(I), T_(A), and T_(B) respectively, and speed, referred to herein as N_(I), N_(A), and N_(B), respectively.

The exemplary engine 14 comprises a multi-cylinder internal combustion engine selectively operative in several states to transfer torque to the transmission 10 via an input shaft 12, and can be either a spark-ignition or a compression-ignition engine. The engine 14 includes a crankshaft (not shown) operatively coupled to the input shaft 12 of the transmission 10. A rotational speed sensor 11 monitors rotational speed of the input shaft 12. Power output from the engine 14, comprising rotational speed and engine torque, can differ from the input speed N_(I) and the input torque T_(I) to the transmission 10 due to placement of torque-consuming components on the input shaft 12 between the engine 14 and the transmission 10, e.g., a hydraulic pump (not shown) and/or a torque management device (not shown).

The exemplary transmission 10 comprises three planetary-gear sets 24, 26 and 28, and four selectively engageable torque-transferring devices, i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutches refer to any type of friction torque transfer device including single or compound plate clutches or packs, band clutches, and brakes, for example. A hydraulic control circuit 42, preferably controlled by a transmission control module (hereafter ‘TCM’) 17, is operative to control clutch states. Clutches C2 62 and C4 75 preferably comprise hydraulically-applied rotating friction clutches. Clutches C1 70 and C3 73 preferably comprise hydraulically-controlled stationary devices that can be selectively grounded to a transmission case 68. Each of the clutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulically applied, selectively receiving pressurized hydraulic fluid via the hydraulic control circuit 42.

The first and second electric machines 56 and 72 preferably comprise three-phase AC machines, each including a stator (not shown) and a rotor (not shown), and respective resolvers 80 and 82. The motor stator for each machine is grounded to an outer portion of the transmission case 68, and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first electric machine 56 is supported on a hub plate gear that is operatively attached to shaft 60 via the second planetary gear set 26. The rotor for the second electric machine 72 is fixedly attached to a sleeve shaft hub 66.

Each of the resolvers 80 and 82 preferably comprises a variable reluctance device including a resolver stator (not shown) and a resolver rotor (not shown). The resolvers 80 and 82 are appropriately positioned and assembled on respective ones of the first and second electric machines 56 and 72. Stators of respective ones of the resolvers 80 and 82 are operatively connected to one of the stators for the first and second electric machines 56 and 72. The resolver rotors are operatively connected to the rotor for the corresponding first and second electric machines 56 and 72. Each of the resolvers 80 and 82 is signally and operatively connected to a transmission power inverter control module (hereafter ‘TPIM’) 19, and each senses and monitors rotational position of the resolver rotor relative to the resolver stator, thus monitoring rotational position of respective ones of first and second electric machines 56 and 72. Additionally, the signals output from the resolvers 80 and 82 are interpreted to provide the rotational speeds for first and second electric machines 56 and 72, i.e., N_(A) and N_(B), respectively.

The transmission 10 includes an output member 64, e.g. a shaft, which is operably connected to a driveline 90 for a vehicle (not shown), to provide output power to the driveline 90 that is transferred to vehicle wheels 93, one of which is shown in FIG. 1. The output power at the output member 64 is characterized in terms of an output rotational speed N_(O) and an output torque T_(O). A transmission output speed sensor 84 monitors rotational speed and rotational direction of the output member 64. Each of the vehicle wheels 93 is preferably equipped with a sensor 94 adapted to monitor wheel speed, V_(SS-WHL), the output of which is monitored by a control module of a distributed control module system described with respect to FIG. 2, to determine vehicle speed, and absolute and relative wheel speeds for braking control, traction control, and vehicle acceleration management.

The input torque from the engine 14 and the motor torques from the first and second electric machines 56 and 72 (T_(I), T_(A), and T_(B) respectively) are generated as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (hereafter ‘ESD’) 74. The ESD 74 is high voltage DC-coupled to the TPIM 19 via DC transfer conductors 27. The transfer conductors 27 include a contactor switch 38. When the contactor switch 38 is closed, under normal operation, electric current can flow between the ESD 74 and the TPIM 19. When the contactor switch 38 is opened electric current flow between the ESD 74 and the TPIM 19 is interrupted. The TPIM 19 transmits electrical power to and from the first electric machine 56 by transfer conductors 29, and the TPIM 19 similarly transmits electrical power to and from the second electric machine 72 by transfer conductors 31 to meet the torque commands for the first and second electric machines 56 and 72 in response to the motor torques T_(A) and T_(B). Electrical current is transmitted to and from the ESD 74 in accordance with whether the ESD 74 is being charged or discharged.

The TPIM 19 includes the pair of power inverters (not shown) and respective motor control modules (not shown) configured to receive the torque commands and control inverter states therefrom for providing motor drive or regeneration functionality to meet the commanded motor torques T_(A) and T_(B). The power inverters comprise known complementary three-phase power electronics devices, and each includes a plurality of insulated gate bipolar transistors (not shown) for converting DC power from the ESD 74 to AC power for powering respective ones of the first and second electric machines 56 and 72, by switching at high frequencies. The insulated gate bipolar transistors form a switch mode power supply configured to receive control commands. There is typically one pair of insulated gate bipolar transistors for each phase of each of the three-phase electric machines. States of the insulated gate bipolar transistors are controlled to provide motor drive mechanical power generation or electric power regeneration functionality. The three-phase inverters receive or supply DC electric power via DC transfer conductors 27 and transform it to or from three-phase AC power, which is conducted to or from the first and second electric machines 56 and 72 for operation as motors or generators via transfer conductors 29 and 31 respectively.

FIG. 2 is a schematic block diagram of the distributed control module system. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and provide coordinated system control of the exemplary hybrid powertrain described in FIG. 1. The distributed control module system synthesizes pertinent information and inputs, and executes algorithms to control various actuators to meet control objectives, including objectives related to fuel economy, emissions, performance, drivability, and protection of hardware, including batteries of ESD 74 and the first and second electric machines 56 and 72. The distributed control module system includes an engine control module (hereafter ‘ECM’) 23, the TCM 17, a battery pack control module (hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module (hereafter ‘HCP’) 5 provides supervisory control and coordination of the ECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface (‘UI’) 13 is signally connected to a plurality of devices through which a vehicle operator controls or directs operation of the electro-mechanical hybrid powertrain. The devices include an accelerator pedal 113 (‘AP’), an operator brake pedal 112 (‘BP’), a transmission gear selector 114 (‘PRNDL’), and a vehicle speed cruise control (not shown). The BP 112 can be directly signally connected to a brake control module (‘BrCM’) 22. The transmission gear selector 114 may have a discrete number of operator-selectable positions, including the rotational direction of the output member 64 to enable one of a forward and a reverse direction.

The aforementioned control modules communicate with other control modules, sensors, and actuators via a local area network (hereafter ‘LAN’) bus 6. The LAN bus 6 allows for structured communication of states of operating parameters and actuator command signals between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus 6 and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality including e.g., antilock braking, traction control, and vehicle stability. Multiple communications buses may be used to improve communications speed and provide some level of signal redundancy and integrity. Communication between individual control modules can also be effected using a direct link, e.g., a serial peripheral interface (‘SPI’) bus (not shown).

The HCP 5 provides supervisory control of the hybrid powertrain, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the user interface 13 and the hybrid powertrain, including the ESD 74, the HCP 5 determines an operator torque request, an output torque command, an engine input torque command, clutch torque(s) for the applied torque-transfer clutches C1 70, C2 62, C3 73, C4 75 of the transmission 10, and the motor torques T_(A) and T_(B) for the first and second electric machines 56 and 72.

The ECM 23 is operatively connected to the engine 14, and functions to acquire data from sensors and control actuators of the engine 14 over a plurality of discrete lines, shown for simplicity as an aggregate bi-directional interface cable 35. The ECM 23 receives the engine input torque command from the HCP 5. The ECM 23 determines the actual engine input torque, T_(I), provided to the transmission 10 at that point in time based upon monitored engine speed and load, which is communicated to the HCP 5. The ECM 23 monitors input from the rotational speed sensor 11 to determine the engine input speed to the input shaft 12, which translates to the transmission input speed, N_(I). The ECM 23 monitors inputs from sensors (not shown) to determine states of other engine operating parameters including, e.g., a manifold pressure, engine coolant temperature, ambient air temperature, and ambient pressure. The engine load can be determined, for example, from the manifold pressure, or alternatively, from monitoring operator input to the accelerator pedal 113. The ECM 23 generates and communicates command signals to control engine actuators, including, e.g., fuel injectors, ignition modules, and throttle control modules, none of which are shown.

The TCM 17 is operatively connected to the transmission 10 and monitors inputs from sensors (not shown) to determine states of transmission operating parameters. The TCM 17 generates and communicates command signals to control the transmission 10, including controlling the hydraulic control circuit 42. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques for each of the clutches, i.e., C1 70, C2 62, C3 73, and C4 75, and rotational output speed, N_(O), of the output member 64. Other actuators and sensors may be used to provide additional information from the TCM 17 to the HCP 5 for control purposes. The TCM 17 monitors inputs from pressure switches (not shown) and selectively actuates pressure control solenoids (not shown) and shift solenoids (not shown) of the hydraulic control circuit 42 to selectively actuate the various clutches C1 70, C2 62, C3 73, and C4 75 to achieve various transmission operating range states, as described hereinbelow.

The BPCM 21 is signally connected to sensors (not shown) to monitor the ESD 74, including states of electrical current and voltage parameters, to provide information indicative of parametric states of the batteries of the ESD 74 to the HCP 5. The parametric states of the batteries preferably include battery state-of-charge, battery voltage, battery temperature, and available battery power, referred to as a range P_(BAT) _(—) _(MIN) to P_(BAT) _(—) _(MAX).

A brake control module (hereafter ‘BrCM’) 22 is operatively connected to friction brakes (not shown) on each of the vehicle wheels 93. The BrCM 22 monitors an operator braking request comprising an operator input through the brake pedal 112 and generates control signals to control the friction brakes and sends a control signal to the HCP 5 to operate the first and second electric machines 56 and 72 based thereon.

Each of the control modules ECM 23, TCM 17, TPIM 19, BPCM 21, and BrCM 22 is preferably a general-purpose digital computer comprising a microprocessor or central processing unit, storage mediums comprising read only memory (‘ROM’), random access memory (‘RAM’), electrically programmable read only memory (‘EPROM’), a high speed clock, analog to digital (‘A/D’) and digital to analog (‘D/A’) circuitry, and input/output circuitry and devices (‘I/O’) and appropriate signal conditioning and buffer circuitry. Each of the control modules has a set of control algorithms, comprising resident program instructions and calibrations stored in one of the storage mediums and executed to provide the respective functions of each computer. Information transfer between the control modules is preferably accomplished using the LAN bus 6 and SPI buses. The control algorithms are executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles are executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation of the hybrid powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event.

The exemplary hybrid powertrain selectively operates in one of several states that can be described in terms of engine states comprising one of an engine-on state (‘ON’) and an engine-off state (‘OFF’), and transmission operating range states comprising a plurality of fixed gears and continuously variable operating modes, described with reference to Table 1, below.

TABLE 1 Engine Transmission Operating Applied Description State Range State Clutches M1_Eng_Off OFF EVT Mode 1 C1 70 M1_Eng_On ON EVT Mode 1 C1 70 G1 ON Fixed Gear Ratio 1 C1 70 C4 75 G2 ON Fixed Gear Ratio 2 C1 70 C2 62 M2_Eng_Off OFF EVT Mode 2 C2 62 M2_Eng_On ON EVT Mode 2 C2 62 G3 ON Fixed Gear Ratio 3 C2 62 C4 75 G4 ON Fixed Gear Ratio 4 C2 62 C3 73

Each of the transmission operating range states is described in the table and indicates which of the specific clutches C1 70, C2 62, C3 73, and C4 75 are applied for each of the operating range states. A first continuously variable mode, i.e., EVT Mode 1, or M1, is selected by applying clutch C1 70 only in order to “ground” the outer gear member of the third planetary gear set 28. The engine state can be one of ON (‘M1_Eng_On’) or OFF (‘M1_Eng_Off’). A second continuously variable mode, i.e., EVT Mode 2, or M2, is selected by applying clutch C2 62 only to connect the shaft 60 to the carrier of the third planetary gear set 28. The engine state can be one of ON (‘M2_Eng_On’) or OFF (‘M2_Eng_Off’). For purposes of this description, when the engine state is OFF, the engine input speed is equal to zero revolutions per minute (‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gear operation provides a fixed ratio operation of input-to-output speed of the transmission 10, i.e., N_(I)/N_(O). A first fixed gear operation (‘G1’) is selected by applying clutches C1 70 and C4 75. A second fixed gear operation (‘G2’) is selected by applying clutches C1 70 and C2 62. A third fixed gear operation (‘G3’) is selected by applying clutches C2 62 and C4 75. A fourth fixed gear operation (‘G4’) is selected by applying clutches C2 62 and C3 73. The fixed ratio operation of input-to-output speed increases with increased fixed gear operation due to decreased gear ratios in the planetary gears 24, 26, and 28. The rotational speeds of the first and second electric machines 56 and 72, N_(A) and N_(B) respectively, are dependent on internal rotation of the mechanism as defined by the clutching and are proportional to the input speed measured at the input shaft 12.

In response to operator inputs via the accelerator pedal 113 and brake pedal 112 as captured by the user interface 13, the HCP 5 and one or more of the other control modules determine torque commands to control the torque generative devices comprising the engine 14 and the first and second electric machines 56 and 72 to meet the operator torque request at the output member 64 and transferred to the driveline 90. Based upon input signals from the user interface 13 and the hybrid powertrain including the ESD 74, the HCP 5 determines the operator torque request, a commanded output torque from the transmission 10 to the driveline 90, an input torque from the engine 14, clutch torques for the torque-transfer clutches C1 70, C2 62, C3 73, C4 75 of the transmission 10; and the motor torques for the first and second electric machines 56 and 72, respectively, as is described hereinbelow.

Final vehicle acceleration can be affected by other factors including, e.g., road load, road grade, and vehicle mass. The engine state and the transmission operating range state are determined based upon a variety of operating characteristics of the hybrid powertrain. This includes the operator torque request communicated through the accelerator pedal 113 and brake pedal 112 to the user interface 13 as previously described. The transmission operating range state and the engine state may be predicated on a hybrid powertrain torque demand caused by a command to operate the first and second electric machines 56 and 72 in an electrical energy generating mode or in a torque generating mode. The transmission operating range state and the engine state can be determined by an optimization algorithm or routine which determines optimum system efficiency based upon operator demand for power, battery state of charge, and energy efficiencies of the engine 14 and the first and second electric machines 56 and 72. The control system manages torque inputs from the engine 14 and the first and second electric machines 56 and 72 based upon an outcome of the executed optimization routine, and system efficiencies are optimized thereby, to manage fuel economy and battery charging. Furthermore, operation can be determined based upon a fault in a component or system. The HCP 5 monitors the torque-generative devices, and determines the power output from the transmission 10 at output member 64 that is required to meet the operator torque request while meeting other powertrain operating demands, e.g., charging the ESD 74. As should be apparent from the description above, the ESD 74 and the first and second electric machines 56 and 72 are electrically-operatively coupled for power flow therebetween. Furthermore, the engine 14, the first and second electric machines 56 and 72, and the electromechanical transmission 10 are mechanically-operatively coupled to transfer power therebetween to generate a power flow to the output member 64.

FIG. 3 shows a control system architecture for controlling and managing signal flow in a hybrid powertrain system having multiple torque generative devices, described hereinbelow with reference to the hybrid powertrain system of FIGS. 1 and 2, and residing in the aforementioned control modules in the form of executable algorithms and calibrations. The control system architecture is applicable to alternative hybrid powertrain systems having multiple torque generative devices, including, e.g., a hybrid powertrain system having an engine and a single electric machine, a hybrid powertrain system having an engine and multiple electric machines. Alternatively, the hybrid powertrain system can utilize non-electric torque machines and energy storage systems, e.g., hydraulic-mechanical hybrid transmissions using hydraulically powered torque machines (not shown).

In operation, the operator inputs to the accelerator pedal 113 and the brake pedal 112 are monitored to determine the operator torque request. The operator inputs to the accelerator pedal 113 and the brake pedal 112 comprise individually determinable operator torque request inputs including an immediate accelerator output torque request (‘Output Torque Request Accel Immed’), a predicted accelerator output torque request (‘Output Torque Request Accel Prdtd’), an immediate brake output torque request (‘Output Torque Request Brake Immed’), a predicted brake output torque request (‘Output Torque Request Brake Prdtd’) and an axle torque response type (‘Axle Torque Response Type’). As used herein, the term ‘accelerator’ refers to an operator request for forward propulsion preferably resulting in increasing vehicle speed over the present vehicle speed, when the operator selected position of the transmission gear selector 114 commands operation of the vehicle in the forward direction. The terms ‘deceleration’ and ‘brake’ refer to an operator request preferably resulting in decreasing vehicle speed from the present vehicle speed. The immediate accelerator output torque request, the predicted accelerator output torque request, the immediate brake output torque request, the predicted brake output torque request, and the axle torque response type are individual inputs to the control system. Additionally, operation of the engine 14 and the transmission 10 are monitored to determine the input speed (‘Ni’) and the output speed (‘No’).

The immediate accelerator output torque request comprises an immediate torque request determined based upon the operator input to the accelerator pedal 113. The control system controls the output torque from the hybrid powertrain system in response to the immediate accelerator output torque request to cause positive acceleration of the vehicle. The immediate brake output torque request comprises an immediate braking request determined based upon the operator input to the brake pedal 112. The control system controls the output torque from the hybrid powertrain system in response to the immediate brake output torque request to cause deceleration, or negative acceleration, of the vehicle. Vehicle deceleration effected by control of the output torque from the hybrid powertrain system is combined with vehicle deceleration effected by a vehicle braking system (not shown) to decelerate the vehicle to achieve the immediate braking request.

The immediate accelerator output torque request is determined based upon a presently occurring operator input to the accelerator pedal 113, and comprises a request to generate an immediate output torque at the output member 64 preferably to accelerate the vehicle. The immediate accelerator output torque request is unshaped, but can be shaped by events that affect vehicle operation outside the powertrain control. Such events include vehicle level interruptions in the powertrain control for antilock braking, traction control and vehicle stability control, which can be used to unshape or rate-limit the immediate accelerator output torque request.

The predicted accelerator output torque request is determined based upon the operator input to the accelerator pedal 113 and comprises an optimum or preferred output torque at the output member 64. The predicted accelerator output torque request is preferably equal to the immediate accelerator output torque request during normal operating conditions, e.g., when any one of antilock braking, traction control, or vehicle stability is not being commanded. When any one of antilock braking, traction control or vehicle stability is being commanded the predicted accelerator output torque request remains the preferred output torque with the immediate accelerator output torque request being decreased in response to output torque commands related to the antilock braking, traction control, or vehicle stability control.

The immediate brake output torque request is determined based upon the operator input to the brake pedal 112 and the control signal to control the friction brakes to generate friction braking torque.

The predicted brake output torque request comprises an optimum or preferred brake output torque at the output member 64 in response to an operator input to the brake pedal 112 subject to a maximum brake output torque generated at the output member 64 allowable regardless of the operator input to the brake pedal 112. In one embodiment the maximum brake output torque generated at the output member 64 is limited to −0.2 g. The predicted brake output torque request can be phased out to zero when vehicle speed approaches zero regardless of the operator input to the brake pedal 112. As desired by a user, there can be operating conditions under which the predicted brake output torque request is set to zero, e.g., when the operator setting to the transmission gear selector 114 is set to a reverse gear, and when a transfer case (not shown) is set to a four-wheel drive low range. The operating conditions whereat the predicted brake output torque request is set to zero are those in which blended braking is not preferred due to vehicle operating factors.

The axle torque response type comprises an input state for shaping and rate-limiting the output torque response through the first and second electric machines 56 and 72. The input state for the axle torque response type can be an active state, preferably comprising one of a pleasability limited state a maximum range state, and an inactive state. When the commanded axle torque response type is the active state, the output torque command is the immediate output torque. Preferably the torque response for this response type is as fast as possible.

Blended brake torque includes a combination of the friction braking torque generated at the wheels 93 and the output torque generated at the output member 64 which reacts with the driveline 90 to decelerate the vehicle in response to the operator input to the brake pedal 112. The BrCM 22 commands the friction brakes on the wheels 93 to apply braking force and generates a command for the transmission 10 to create a negative output torque which reacts with the driveline 90 in response to the immediate braking request. Preferably the applied braking force and the negative output torque can decelerate and stop the vehicle so long as they are sufficient to overcome vehicle kinetic power at wheel(s) 93. The negative output torque reacts with the driveline 90, thus transferring torque to the electromechanical transmission 10 and the engine 14. The negative output torque reacted through the electromechanical transmission 10 can be transferred to the first and second electric machines 56 and 72 to generate electric power for storage in the ESD 74.

A strategic optimization control scheme (‘Strategic Control’) 310 determines a preferred input speed (‘Ni_Des’) and a preferred engine state and transmission operating range state (‘Hybrid Range State Des’) based upon the output speed and the operator torque request and based upon other operating parameters of the hybrid powertrain, including battery power limits and response limits of the engine 14, the transmission 10, and the first and second electric machines 56 and 72. The predicted accelerator output torque request and the predicted brake output torque request are input to the strategic optimization control scheme 310. The strategic optimization control scheme 310 is preferably executed by the HCP 5 during each 100 ms loop cycle and each 25 ms loop cycle. The desired operating range state for the transmission 10 and the desired input speed from the engine 14 to the transmission 10 are inputs to the shift execution and engine start/stop control scheme 320.

The shift execution and engine start/stop control scheme 320 commands changes in the transmission operation (‘Transmission Commands’) including changing the operating range state based upon the inputs and operation of the powertrain system. This includes commanding execution of a change in the transmission operating range state if the preferred operating range state is different from the present operating range state by commanding changes in application of one or more of the clutches C1 70, C2 62, C3 73, and C4 75 and other transmission commands. The present operating range state (‘Hybrid Range State Actual’) and an input speed profile (‘Ni_Prof’) can be determined. The input speed profile is an estimate of an upcoming input speed and preferably comprises a scalar parametric value that is a targeted input speed for the forthcoming loop cycle. The engine operating commands and the operator torque request are based upon the input speed profile during a transition in the operating range state of the transmission.

A tactical control scheme (‘Tactical Control and Operation’) 330 is repeatedly executed during one of the control loop cycles to determine engine commands (‘Engine Commands’) for operating the engine 14, including a preferred input torque from the engine 14 to the transmission 10 based upon the output speed, the input speed, and the operator torque request comprising the immediate accelerator output torque request, the predicted accelerator output torque request, the immediate brake output torque request, the predicted brake output torque request, the axle torque response type, and the present operating range state for the transmission. The engine commands also include engine states including one of an all-cylinder operating state and a cylinder deactivation operating state wherein a portion of the engine cylinders are deactivated and unfueled, and engine states including one of a fueled state and a fuel cutoff state. An engine command comprising the preferred input torque of the engine 14 and a present input torque (‘Ti’) reacting between the engine 14 and the input member 12 are preferably determined in the ECM 23. Clutch torques (‘Tcl’) for each of the clutches C1 70, C2 62, C3 73, and C4 75, including the presently applied clutches and the non-applied clutches are estimated, preferably in the TCM 17.

An output and motor torque determination scheme (‘Output and Motor Torque Determination’) 340 is executed to determine the preferred output torque from the powertrain (‘To_cmd’). This includes determining motor torque commands (‘T_(A)’, ‘T_(B)’) to transfer a net commanded output torque to the output member 64 of the transmission 10 that meets the operator torque request, by controlling the first and second electric machines 56 and 72 in this embodiment. The immediate accelerator output torque request, the immediate brake output torque request, the present input torque from the engine 14 and the estimated applied clutch torque(s), the present operating range state of the transmission 10, the input speed, the input speed profile, and the axle torque response type are inputs. The output and motor torque determination scheme 340 executes to determine the motor torque commands during each iteration of one of the loop cycles. The output and motor torque determination scheme 340 includes algorithmic code which is regularly executed during the 6.25 ms and 12.5 ms loop cycles to determine the preferred motor torque commands.

The hybrid powertrain is controlled to transfer the output torque to the output member 64 to react with the driveline 90 to generate tractive torque at wheel(s) 93 to forwardly propel the vehicle in response to the operator input to the accelerator pedal 113 when the operator selected position of the transmission gear selector 114 commands operation of the vehicle in the forward direction. Similarly, the hybrid powertrain is controlled to transfer the output torque to the output member 64 to react with the driveline 90 to generate tractive torque at wheel(s) 93 to propel the vehicle in a reverse direction in response to the operator input to the accelerator pedal 113 when the operator selected position of the transmission gear selector 114 commands operation of the vehicle in the reverse direction. Preferably, propelling the vehicle results in vehicle acceleration so long as the output torque is sufficient to overcome external loads on the vehicle, e.g., due to road grade, aerodynamic loads, and other loads.

FIG. 4 shows a control system architecture for managing signal flow in the distributed control system to effect tractive braking through one or more of the vehicle wheels 93, described with reference to the hybrid powertrain described hereinabove. The operator braking request that is input to the brake pedal 112 (‘Operator Braking Request’) is monitored by the BrCM 22 which preferably comprises the immediate brake output torque request from which the BrCM 22 can determine a total braking torque request (‘Total Braking Torque Request’). The BrCM 22 generates a regenerative braking axle torque request (‘Regenerative Braking Axle Torque Request’) based upon the total braking torque request and a regenerative braking axle torque capacity (‘Regenerative Braking Axle Torque Capacity’) and any presently applied regenerative braking torque (‘Estimated Regen Braking Achieved Torque’). The regenerative braking axle torque request preferably comprises the predicted brake output torque request described hereinabove with reference to FIG. 3. The BrCM 22 generates a control signal (‘Friction Brake Control’) to control the actuable friction brake in each of the wheels 93 based upon a difference between the operator braking request and the regenerative braking torque that can be reacted through the transmission 14 by operation of the first and second electric machines 56 and 72 as estimated by the HCP 5. The BrCM 22 acts as a master arbitrator for controlling the friction brakes and the transmission 10 to meet the operator braking request.

The HCP 5 determines the regenerative braking axle torque capacity, which is a torque-based measurement of the ability of the transmission 10 to react torque from the driveline 90 through the selectively applied clutches C1 70, C2 62, C3 73, and C4 75 to the first and second electric machines 56 and 72, limited by the maximum brake output torque. The HCP 5 estimates the presently applied regenerative braking torque reacted from the driveline 90 and the output member 64 of the transmission 10, and communicates the regenerative braking axle torque capacity and the regenerative braking torque to the BrCM 22. The HCP 5 determines the preferred output torque from the powertrain (‘To_cmd’) through the motor torque control scheme 340 and generates the motor torque commands (‘T_(A)’, ‘T_(B)’) for controlling the first and second electric machines 56 and 72 based upon the regenerative braking axle torque request utilizing the control architecture described with reference to FIGS. 3 and 4.

The timing sequence of transmitting signals from the brake pedal 112 to the BrCM 22 and subsequently to the HCP 5 is intentional, as the most currently available operator input to the brake pedal can be used to control braking during a braking event. The HCP 5 leverages recuperation of kinetic energy through regenerative braking to generate storable electric power and improve operating efficiency.

The control system is described hereinabove with reference to an embodiment including the engine 14 and the first and second electric machines 56 and 72 mechanically connected to the electromechanical transmission 10. Alternatively, the control system can be used with other transmission systems having torque-generative machines and energy storage systems which can controllably react torque through a driveline to effect tractive braking, preferably those that use the reactive torque through the driveline to generate storable power for subsequent use, e.g., in the form of stored electric power, stored hydraulic power, or stored mechanical power.

It is understood that modifications are allowable within the scope of the disclosure. The disclosure has been described with specific reference to the preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the disclosure. 

The invention claimed is:
 1. An apparatus, comprising: an internal combustion engine mechanically coupled to a transmission device operative to transfer mechanical power between the engine and a second power generating device and an output member mechanically coupled to a driveline to transmit tractive torque to a wheel including an actuable friction brake; a brake control module operatively connected to the actuable friction brake; a second control module operatively connected to the internal combustion engine and the transmission device; and a brake pedal; the second control module configured to: determine a regenerative braking axle torque capacity comprising an ability of the transmission device to react torque transferred from the driveline through an applied clutch to the second power generating device, said regenerative braking axle torque capacity limited to a maximum brake output torque, determine a regenerative braking torque presently applied to the driveline through the output member of the transmission device, communicate the regenerative braking axle torque capacity and the regenerative braking torque to the brake control module, and generate a control signal to command a power output from the second power generating device based upon a regenerative braking axle torque request, said regenerative braking axle torque request comprising an optimum brake output torque at the output member; and the brake control module configured to: determine a total braking torque request based upon an operator input to the brake pedal, generate the regenerative braking axle torque request based upon the total braking torque request, the regenerative braking axle torque capacity, and the regenerative braking torque presently applied to the driveline, generate a control signal to control the actuable friction brake based upon a difference between the total braking torque request and the regenerative braking torque presently applied to the driveline, and monitor a speed of the wheel and phase out the regenerative braking axle torque request when the speed of the wheel approaches zero; and set the regenerative braking axle torque request to zero torque when a gear selector switch is set to a reverse gear.
 2. The apparatus of claim 1, further comprising the second control module configured to generate a control signal to command a power output from the second power generating device based upon-the regenerative braking axle torque request and limited by the regenerative braking axle torque capacity.
 3. An apparatus, comprising: an internal combustion engine; an electric machine; a transmission device including selectively applied clutches and an output member; the internal combustion engine and the electric machine mechanically coupled to the transmission device; the output member mechanically coupled to a driveline; the driveline including a wheel including an actuable friction brake; the transmission configured to react torque from the driveline to the output member through the selectively applied clutches to the electric machine; a brake control module operatively connected to the actuable friction brake; a second control module operatively connected to the internal combustion engine and the transmission; and a brake pedal; the second control module configured to: determine a regenerative braking axle torque capacity, determine a regenerative braking axle torque capacity comprising an ability of the transmission device to react torque transferred from the driveline through the selectively applied clutches to the electric machine, said regenerative braking axle torque capacity limited to a maximum brake output torque, determine a magnitude of torque reacted from the driveline to the output member of the transmission device, communicate the regenerative braking axle torque capacity and the magnitude of the torque reacted from the driveline to the brake control module, and generate a control signal to command a power output from the electric machine based upon a regenerative braking axle torque request, said regenerative braking axle torque request comprising an optimum brake output torque at the output member; the brake control module configured to: determine a total braking torque request based upon an operator input to the brake pedal, generate the regenerative braking axle torque request based upon the total braking torque request, the regenerative braking axle torque capacity, and the magnitude of the reacted torque, said regenerative braking axle torque request comprising an optimum brake output torque at the output member, generate a control signal to control the actuable friction brake based upon a difference between the total braking torque request and the magnitude of the reacted torque, and monitor a speed of the wheel and phase out the regenerative braking axle torque request when the speed of the wheel approaches zero; and set the regenerative braking axle torque request to zero torque when a gear selector switch is set to a reverse gear.
 4. The apparatus of claim 3, further comprising the second control module configured to generate a control signal to command a power output from the electric machine based upon the regenerative braking axle torque request and limited by the regenerative braking axle torque capacity.
 5. The apparatus of claim 3, further comprising the electric machine operative to transform the torque reacted from the driveline to electric power; and an energy storage device connected to the electric machine operative to store the electric power as electric energy potential.
 6. A method to operate a powertrain system including an engine mechanically coupled to a transmission and a power generating device electrically connected to an energy storage device, the transmission operative to transfer mechanical power between the engine and the power generating device and an output member coupled to a driveline to transmit tractive torque to a wheel, the wheel including an actuable friction brake and the power generating device operative to react tractive torque transferred from the wheel through the driveline to the transmission said method being performed by a microprocessor, the method comprising: monitoring an operator input to a brake pedal with a first control module; determining a regenerative braking axle torque capacity with a second control module, said regenerative braking axle torque capacity comprising an ability of the transmission device to react torque transferred from the driveline through the selectively applied clutches to the electric machine, said regenerative braking axle torque capacity limited to a maximum brake output torque; determining a regenerative braking torque transmitted between the driveline and the output member of the transmission device with the second control module; communicating the regenerative braking axle torque capacity and the regenerative braking torque to the first control module; generating a control signal to command a power output from the second power generating device based upon a regenerative braking axle torque request with the second control module, said regenerative braking axle torque request comprising an optimum brake output torque at the output member; determining a total braking torque request based upon the operator input to the brake pedal with the first control module; generating the regenerative braking axle torque request based upon the total braking torque request, the regenerative braking axle torque capacity, and the regenerative braking torque with the first control module; generating a control signal to control the actuable friction brake based upon a difference between the total braking torque request and the regenerative braking torque with the first control module; monitoring a speed of the wheel and phasing out the regenerative braking axle torque request when the speed of the wheel approaches zero; and setting the regenerative braking axle torque request to zero torque when a gear selector switch is set to a reverse gear.
 7. The method of claim 6, further comprising connecting an energy storage device to the electric machine; transforming the regenerative braking torque transmitted between the driveline and the output member of the transmission device to electric power; and storing the electric power as electric energy potential. 